Stripped bearing plate screw holes on Power Kraft Lathe

Jorje_villafan · Oct 18, 2017

Well I'm super new to the metal working world and recently acquired an old Power Kraft Lathe (Logan, as I'm sure most of you may know). As I was taking it apart to clean it, the bearing cover screws, while they seemed snug in their homes upon first loosening, soon spun freely in place with the exception one which backed out all the way, but after further investigation, saw that all 3 screw holes were stripped and I could (after using a strong magnet top get them out) just push them all the way in without spinning. That seems to be (in my limited knowledge) the only issue that needs serious attention with this lathe.. Pretty sure re-tapping is not and option as the heads cannot be larger, as they fit snugly into a recess.

So my question is, is there a way that you machinist fellas and fellettes handle this situation? Epoxy maybe? I don't wanna try anything without getting some seasoned advice!

Thanks!

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TGTool · Oct 18, 2017

You don't give a size, but Helicoil is often an option.

With pictures there might be more suggestions. It sounds like the current screw heads are countersunk since you say "they fit snugly into a recess" but I don't know if that means they can't be counterbored oversize.

Jorje_villafan · Oct 18, 2017

Hey thanks for the reply TGTool!

Well, I don't have a thread gauge, but the threads are about ¼“ in diameter and maybe like 20 threads per inch. It's a common size, as I have many others in different lengths and head types in my nut and bolt boxes...

As for the recess, in the attached pic, you can see the recess is part of the bearing cover. Seems to me that there is limited space for altering the recess. I will look into that helicoil product you mentioned..

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iwananew10K · Oct 18, 2017

First option is the same size screws but longer, the holes are probably tapped quite a bit deeper than the original screws.

EDIT- you may find this useful...part #0168 - 5/16"x18tpi fillister head screw,5/8" long.

http://vintagemachinery.org/pubs/657/17185.pdf

ewlsey · Oct 18, 2017

Do it the millwright way:

Cover bolt in Loctite (red is always best). Pound bolt into hole with hammer. Take a 45 minute coffee break. Repeat for other two bolts. Hand off to second shift.

JST · Oct 18, 2017

Nonsense.

They are simply the wrong screws, they should be 5/16-18, not 1/4-20. It is perfectly credible that they should nearly fit, but actually come out, as 0.250 vs 0.312 is a bit of a difference, and 18 vs 20 might appear to fit over a short distance, particularly if the screws are too small.

Had a look at the Logan in my shop. It has 5/16-18 x 0.7" Allen-head screws. I had to turn down the heads to fit them in the spots which originally had "fillister head" screws.

Those screws are required, because that is not just a cover, it holds the snap-ring of the double-row preloaded nose bearing, and without that being held securely, the thing will chatter like a tree full of squirrels.

Get some 5/16-18 screws of 5/8" length. I doubt you can find fillister head, but any fairly small head will allow you to hold the ring down and use the lathe. A chuck with a backplate ought to fit over the heads. Then you need to turn down some Allen-head screws to fit in the recesses, and put them in.

atomarc · Oct 19, 2017

ewlsey said:
Do it the millwright way:

Cover bolt in Loctite (red is always best). Pound bolt into hole with hammer. Take a 45 minute coffee break. Repeat for other two bolts. Hand off to second shift.

You must be working with the wrong Millwrights...the Peoria Millwrights.

Stuart

Jorje_villafan · Oct 19, 2017

Thank you to everyone who has chimed in! Turns out that it was super simple! JST nailed it!! The little screw was the culprit. After dinner, I looked at the manual that iwananew10k linked to and did take notice of the screw size differences in the diagram. However, I was gonna wait until tomorrow to look into it. Then after I read JST's reply, I soo excited about the possible easy fix, I walked out to the shop and dug up a few 5/16x18 bolts and tried 'em out and they worked perfectly! I'll check to see if I can find a bolt with a proper fitting head at the hardware store. If not then I'll do exactly as JST suggested. It'll be my first metal lathe project.

Also, I found out that the there is a slight misalignment if the cover isn't aligned with the correct hole in the housing, which is probably why someone might have chose the smaller screws.

Anyways, thank you again!! I really appreciate the assistance!!

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TGTool · Oct 19, 2017

JST said:
Get some 5/16-18 screws of 5/8" length. I doubt you can find fillister head, but any fairly small head will allow you to hold the ring down and use the lathe. A chuck with a backplate ought to fit over the heads. Then you need to turn down some Allen-head screws to fit in the recesses, and put them in.

Or chuck your new screws in a hand drill and hold the heads against your grinder wheel. The OD doesn't need to be precise, just fit easily in the counterbores (where your hack grinder job will be neatly hidden).

JST · Oct 19, 2017

Ja, I might actually have done something like that, the OD looked more ground. Probably done on the belt/disk sander, actually.

iwananew10K · Oct 19, 2017

5/16-18x5/8 Fillister Head Slotted Machine Screws Steel Zinc Plated (1) | eBay

or slightly longer just in case-
5/16-18x3/4 Fillister Head Slotted Machine Screws Steel Zinc Plated (1) | eBay

Jorje_villafan · Oct 20, 2017

Hey Thanks again for all of your replies! Here's just a few follow up pics to show the completed fix! I ended up using TGTool's idea of using the hand drill and grinding wheel vs chucking them up in the lathe. Mainly because I need to swap out the power and fwd/Rev cords on the lathe to run it.

Cost: $1.05
Time: less than 5 minutes (not included this thread activity and other internet related searches)

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plastikdreams · Oct 20, 2017

Nice! Sometimes it's just that easy.

iwananew10K · Oct 20, 2017

Good job...especially of asking before something got permanantly damaged!

More than can be said for many.

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